PROJECT 3 PROJECT SUMMARY The goal of the work in this Project is to understand the mechanisms of salt-sensitive hypertension. Salt-induced hypertension and renal injury in Dahl Salt-Sensitive (SS) rats fed a high salt diet proceeds in two phases. An initial, primary rise of blood pressure (BP), which is not dependent upon inflammation, is followed by a more dramatic, secondary rise of BP which is accompanied by increased infiltration of immune cells into the kidney and culminates in `malignant hypertension'. Pharmacological and genetic approaches that reduce renal immune cell infiltration attenuate this secondary phase of salt-induced hypertension and renal injury in SS rats. These observations parallel data obtained from hypertensive patients and indicate that immune cells in the kidney play a key role in the pathology of hypertension by amplifying the disease process, but the mechanisms leading to the infiltration and activation of immune cells in the kidney are unknown and are the focus of this research proposal. In the present proposal, we present intriguing data indicating that an initial elevation of renal perfusion pressure (RPP) elicits a molecular cascade involving increased H2O2, increased mTORC1, and activation of the NLRP3 inflammasome. Moreover, our data indicate that H2O2 and mTORC1 can activate the inflammasome which mediates infiltration of immune cells into the kidney. Based on these data, we hypothesize that malignant hypertension and renal damage in SS rats is triggered by a primary elevation of RPP which leads to an associated increase of renal oxidative stress (H2O2 from Nox4) and mTORC1. The altered H2O2 and mTORC1 activate the NLRP3 inflammasome which mediates innate and adaptive immune mechanisms. The resulting infiltrating immune cells then release additional H2O2 from Nox2 in a positive feedback cycle that further enhances hypertension and renal damage. This hypothesis will be tested in three Specific Aims: Aim 1 will test the hypothesis that the NLRP3 inflammasome, stimulated by increased H2O2 and increased mTORC1, mediates innate and adaptive immune responses in the SS following an elevation of sodium intake and results in the infiltration of activated T-lymphocytes into the kidney which amplify salt-sensitive hypertension and renal damage. Aim 2 will test the hypothesis that elevated renal perfusion pressure increases intrarenal H2O2 and mTORC1 which serve to stimulate the NLRP3 inflammasome and T-cell infiltration in the SS kidney when fed high salt. Aim 3 will test the hypothesis that T-cell infiltration into the kidney enhances H2O2 production and inflammasome activation which amplifies hypertension by decreasing GFR and increasing sodium reabsorption to further alter pressure natriuresis resulting in malignant hypertension. This proposal, which is addressing a significant health problem, is conceptually and technically innovative, utilizes a set of unique experimental approaches, and is highly dependent upon the expertise provided by the other investigators in Projects 1 and 2 and Cores A, B, and C of this PPG.